ACA and YOU : Chapter 7

ACA Standards

1. Keywords

Keywords may be used in Aristocrats, Patristocrats, Cryptarithms,
Xenocrypts, and in many Cipher Exchange systems. Although a key may be
optional, its use is recommended as it is a useful aid to solution.

Four basic schemes are referred to by number, K1 to K4. The alphabet is
keyed by writing an arbitrary keyword or phrase FOLLOWED (underlined
"followed") by the rest of the alphabet in NORMAL (underlined "normal")
order. A letter occurring more than once is omitted after the first
occurrence.

e.g. CONSTELLATION becomes CONSTELAI.

Either the plaintext or the ciphertext alphabet may be shifted ("wrapped
round") to avoid a plaintext letter standing for itself in simple
substitutions.

Mixed Alphabetic Keyword Types

The keyed alphabets may be mixed rather than in normal sequence. The
resulting keys are identified as K1M, K2M, etc. The mixing is done with a
transposition block, and the mixed alphabet is taken off by columns, either
in l-r sequence or in alphabetical order of the top letters (a key):

Other arrangements submitted will ordinarily be returned to the author for
re-encipherment, or will be discarded. With a proper choice of keyword,
these systems have been found sufficient for a wide range of difficulty or
keyword recovery. When keywords are used as an adjunct of plaintext
recovery, these systems give enough play of possibilities.
Rarely, an improperly keyed problem will be printed with a key designation,
or it may be labeled "Variant", as in "K2V". This is used if the alphabet
is split around the keyword, e.g.

A B C K E Y D F G H I L ... Z
^ ^ ^

2. Standard Features of Ciphers

Aristocrats, Patristocrats, and Xenocrypt Substitutions

1. Length:75-100 letters(85-120 for Xenos). Pats should be 90-
105, and in no case less than 85 or more than 140.
2. No more than 3 singletons (letters used only once).
3. At least 18 different letters should be used in each
problem.
4. Repeated consecutive plaintext should be avoided.
5. No more than 3 proper nouns, each indicated by "*" at the
left.

CRYPTARITHMS

1. Single or double keyed problems in division, multiplication,
square roots and various equations are popular.
2. Additions should have no more than 3 terms plus the total.
3. Equations should have no more than 3 items.
4. Multiplications should have no more than 3 digits in the
multiplier.
5. Divisions must not end in zero to be brought down as
remainder unless a legitimate subtraction follows from it
in the last step.
6. Problems must show all steps involved, not just components
and answers.
7. Keywords MUST be complete (CRYPTAIM is not acceptable).
8. Several words may be used together (HOWISFRANK is
acceptable).
9. Number-bases should be in the range 8-16.

CIPHER EXCHANGE

The acceptable lengths for Cipher Exchange ciphers are given with each
cipher in Chapter 8.

XENOCRYPTS

Xenos use Dutch, Esperanto, French, German, Latin, Italian, Portuguese,
Spanish and Scandinavian languages. Other languages may be used, often as
Specials.

HYPHENS and WORD BREAKS

When a ciphertext contains word divisions and occupies more than one
line when printed, there can be ambiguity as to whether a word at the end
of a line is complete or not. To avoid confusion, use these conventions:

Use the single "-" when a word is split at the end of a line this does
not indicate proper syllabic hyphenation.

Use a double hyphen "=" if the word is hyphenated in the plaintext.

3. Computer Usage

For details of preferred computer languages for articles, disk formats
for exchange, variable names for listings, etc., please refer to the "Note
To Authors" section in any copy of the "Computer Supplement".